1. Field of the Invention
This invention relates to methods and means for determining a substance in a liquid based on its affinity for a specific binding partner. In one aspect, therefore, the present invention relates to binding assays of the immunological type for determining antigens and haptens or their antibodies. In a preferred embodiment, the present invention relates to radioimmunoassay (RIA) methods and means for detecting hepatitis B surface (HB.sub.s) antigen in serum and plasma samples.
There is an ever increasing interest in improving specific binding assay techniques and test means. Classical RIA techniques involve competition between sample antigen and radiolabeled antigen for binding with a specific antibody. The amount of radioactivity which becomes associated with the antibody is a function of sample antigen concentration and can be determined by precipitating, and thereafter separating, the radioactive antigen-antibody complex, or more conveniently, by using an insoluble form of antibody such as antibody coupled to solid particles or matrices. Recently, several alternative labeling materials have been reported for replacement of radioisotopes, including enzymes, coenzymes, enzyme substrates, fluorescent molecules, molecules capable of participating in light producing reactions, and enzyme modulators.
There is a particular need for a more advantageous specific binding assay technique for detecting hepatitis B surface (HB.sub.s) antigen in samples of serum or plasma. It is well accepted that a patient can contract hepatitis after receiving a transfusion of blood containing HB.sub.s antigen. Until recently, a wide variety of techniques were used routinely by hospital laboratories and blood banks to detect HB.sub.s antigen in blood drawn for transfusion purposes. Such techniques included immunodiffusion, complement fixation, counterelectrophoresis, latex agglutination, hemagglutination, and RIA. Recently, it has become a requirement in the United States that blood drawn for transfusion be tested for hepatitis by the most sensitive assay techniques available. RIA methods have since become the most widely used for detecting HB.sub.s antigen.
2. Description of the Prior Art
Several specific binding assay techniques have evolved which make use of nonspecific binders or adsorbents. Such specific binding-adsorbent assays fall into two distinct categories: